Graphics processing apparatus for producing output data at edges of an output image defined by vector data

Abstract

A graphics processing apparatus carries out an antialiasing for obtaining an output image having smooth edges, enabling a speedy computation of approximate shading area rates of pixels by making use of neither a subpixel dividing process nor a shading pixel counting process. The apparatus comprises a discriminating part for discriminating the presence of an end point pixel at an edge portion of an image defined by a vector data, a computing part for computing the number of edge pixels by extracting two integer parts a, b from x coordinate values Xa, Xb of two points where a scanline intersects the vector data, a setting part for setting a x coordinate value of the end point pixel to the Xb only when an end point pixel is found at the edge portion, an approximate point part for determining an approximate point value C' from a prescribed factor c×(n-1) computed by a decimal fraction c extracted from the x coordinate value Xa, a memory part for storing a lookup table containing a set of predetermined data, and an approximate area factor part for determining an approximate shading area factor k by making reference to the lookup table stored in the memory part.

What is claimed is 
     
       1. A graphics processing apparatus for producing output data at edges of an output image which is defined by vector data, the apparatus comprising: a) approximation means for determining an approximate area factor of each edge pixel at edges of the output image, which output image is defined by the vector data, the determining being based on a decimal fraction extracted from a coordinate value of a predetermined one of two points, which two points are intersections between the vector data and two border lines of a scanline having a thickness equivalent to a width of one pixel; and   b) antialiasing means, including: 1) means for determining shaded area factors of the edge pixels of the output image, based on the approximate area factor of each edge pixel determined by the approximation means; and   2) means for producing output data based on the shaded area factors, so as to reduce aliasing effects at edges of the output image.     
     
     
       2. The apparatus as claimed in claim 1, wherein: said approximation means includes means for extracting a decimal fraction from an x coordinate value of either of said two points to determine said approximate area factor.   
     
     
       3. The apparatus as claimed in claim 1, wherein: said approximation means includes means for extracting a decimal fraction from a y coordinate value of either of said two points to determine said approximate area factor.   
     
     
       4. The apparatus as claimed in claim 1, wherein said approximation means extracts a decimal fraction from a x coordinate value or y coordinate value of a prescribed point selected from said two points, and determines an approximate area factor to be assigned to each said edge pixels on the basis of an edge character data, said edge character data including a first data indicative of whether the number of said edge pixels is singular or plural, a second data indicative of whether said edge pixels are located on a right side of the output image or on a left side thereof, and a third data indicative of whether said edge pixels are located on a top side of the output image or on a bottom side thereof. 
     
     
       5. The apparatus as claimed in claim 1, further comprising extraction means for extracting a decimal fraction from a x coordinate value of a point out of said two points where the vector data is intersected by a scanline, said point being located nearer to the output image, and discrimination means for discriminating an edge pixel type indicative of whether said edge pixels are located on a right side of the output image or on a left side thereof, wherein said approximation means determines an approximate area factor of a first pixel nearest to the output image among said edge pixels, on the basis of the edge pixel type from said discrimination means and the decimal fraction from said extraction means. 
     
     
       6. The apparatus as claimed in claim 5, wherein said approximation means determines approximate area factors of second pixels to be equal to zero, said second pixels being different from said first pixel among said edge pixels. 
     
     
       7. The apparatus as claimed in claim 5, further comprising second approximation means for determining successively approximate area factors of second pixels among said edge pixels by using said approximate area factor of said first pixel as a reference value, said second pixels being pixels among said edge pixels which are different from said first pixel. 
     
     
       8. The apparatus as claimed in claim 7, wherein said second approximation means determines successively the approximate area factors of the second pixels until a resulting value of an approximate area factor from said second approximation means is found equal to zero, or until an approximate area factor of a final pixel among said edge pixels is determined by said second approximation means. 
     
     
       9. The apparatus as claimed in claim 7, wherein the approximate area factors of the second pixels are successively determined by said second approximation means by applying repeatedly a formula: ks-1/(n-1) to each said second pixel, where n is the number of different levels indicating the approximate area factors of pixels and ks is the reference value being initially represented by the approximate area factor of the first pixel from said approximation means. 
     
     
       10. A graphics processing apparatus for producing output data at edges of an output image which is defined by vector data, the apparatus comprising; a) first checking means for determining a total number of edge pixels at edges of the output image which is defined by the vector data, based on coordinate values of two points where the vector data is intersected by two border lines of a scanline having a thickness equivalent to a width of one pixel;   b) edge pixel means for discriminating an edge pixel type of the output image, the edge pixel type indicating whether the edge pixels are located on a right side of the output image or on a left side of the output image;   c) decimal fraction means including: 1) means for extracting a decimal fraction from a coordinate of a predetermined one of the two points, the predetermined one point being located nearer to the output image defined by the vector data; and   2) means for converting the decimal fraction into an approximate value;     d) memory means for storing area factor information including a plurality of approximate area factors relating to a plurality of successive pixels of the output image, each of the approximate area factors being predetermined based on (1) the total number determined by the first checking means, (2) the approximate value produced by the decimal fraction means, and (3) the edge pixel type discriminated by the edge pixel means;   e) control means including: 1) means for reading out the area factor information from the memory means based on (1) the total number discriminated by the first checking means, (2) the approximate value produced by the decimal fraction of means, and (3) the edge pixel type discriminated by the edge pixel means; and   2) means for determining an approximate area factor of each of the edge pixels of the output image based on the area factor information; and     f) antialiasing means including: 1) means for determining shaded area factors of the edge pixels of the output image, based on the approximate area factor of each edge pixel determined by the control means; and   2) means for producing output data based on the shaded factors, so as to reduce aliasing effects at edges of the output image.     
     
     
       11. The apparatus as claimed in claim 10, further comprising end point means for discriminating the presence of an end point of the vector data in the edge pixels at an end portion of the output image, wherein said control means determines the number of the edge pixels on the basis of a x coordinate value of the end point and a x coordinate value of a point out of said two points.